The purpose of this project is to determine the effect of various interventions commonly associated with cardiopulmonary bypass on blood flow to various depths in the ventricular and septal walls. Interventions to be studied include inotrophic and vasoactive drugs, ventricular decompression and distention, normal and hypertrophied left and right ventricle, hypothermia aortic clamping, during fibrillation and sinus rhythms. Radionuclide labeled microscopheres will be used to study the distribution of blood flow. Myocardial oxygen consumption and distribution of isehemic lesions will be related to distribution of blood flow.